A torque motor is an inductive device that is controlled with a current based driver circuit. Torque motors can be used in any number of applications using pneumatic devices that need controllable flow. Examples of devices which employ torque motors are bleed systems, anti-icing systems, engine control systems, environmental control systems, and air management systems. The torque motor responds to the difference in pressure between the supply and demand sides to provide a regulated air flow. It provides more flow when more current is supplied to it. In this way, the flow is related to the current and can be regulated by using a driver with an adjustable current output.
Torque motor drivers are generally one of two types: linear voltage controlled current drivers and pulse width modulation (PWM) drivers. PWM drivers can use both a positive and negative voltage rail, but they have greater electromagnetic noise interference problems, require more sophisticated control techniques, and use more parts and layout space. Linear voltage controlled devices are simpler to implement and have better noise characteristics, which make them a preferred method in many implementations of a torque motor driver. A 50 mA current driver may supply 0 mA to the load at a command in put voltage of 0V, 25 mA at 2.5 V, and 50 mA at 5V, etc.
Known linear voltage controlled current drivers are driven by a positive voltage signal and powered by a positive voltage rail. Typical values are 0-5V input signals and 15-19 volt rails.